1. Choi YY, Park JS, Park SY, Kim HJ, Yeo J, Kim JC, et al. Can intravenous patientcontrolled analgesia be omitted in patients undergoing laparoscopic surgery for colorectal cancer? Ann Surg Treat Res. 2015; 88:86–91.
2. Hurley RW, Murphy JD, Wu CL. Acute postoperative pain. In : Miller RD, editor. Miller's anesthesia. 8th ed. Philadelphia: Elsevier Churchill Livingstone;2015. p. 2974–2998. .
3. Vazzana M, Andreani T, Fangueiro J, Faggio C, Silva C, Santini A, et al. Tramadol hydrochloride: pharmacokinetics, pharmacodynamics, adverse side effects, coadministration of drugs and new drug delivery systems. Biomed Pharmacother. 2015; 70:234–238.
4. Murphy JD, Yan D, Hanna MN, Bravos ED, Isaac GR, Eng CA, et al. Comparison of the postoperative analgesic efficacy of intravenous patient-controlled analgesia with tramadol to intravenous patient-controlled analgesia with opioids. J Opioid Manag. 2010; 6:141–147.